I cut quilt backs all the time so cutting long multiple lengths of fabric should be something I do with finesse. But more often than not, when the back measures more than 60 inches, I find my 2 cut pieces of fabric are 1/4 to 1 inch different in length, even when I thought I had measured accurately. It never bothers me much. I make sure the top edge of the quilt back is straight across so that the quilt layer is straight. I don't worry about the uneven lengths at the bottom. They'll be trimmed off once all the quilting is done.

But this summer I made curtains for the windows of the gym at my church. They are big, double width windows. My fabric cuts needed to be accurate from the start. The curtains were just too large to try to even things up as I went.

So I set up a cutting station on my attic floor. I have lots of space up there so it was perfect. But I could also have done this in a long hall.

My fabric cuts were much more accurate using this method. It looks complicated but it only takes a couple minutes to do the set up.

To set up a cutting station on the floor

Make sure the floor is really clean! Vacuum it and then dry mop.
Using painters tape make a straight line at the top end of your cutting area. Make sure it is straight.
With a tape measure measure out the length of fabric to be cut. I use a metal carpenter's tape because it's stiff and stays in one place.
Place a large cutting mat, a least the width of your fold fabric under the tape so that the cutting line will be in the middle of the mat. Make sure the mat is straight. I used the flooring as a guide. Tape the cutting mat down to the floor with painters tape.
Now set up a cutting line on the mat. Measure the exact length you need to cut from at least 3 places along the length of the tape you placed in step 2.
Mark the cutting length with painter's tape across the width of the cutting mat. Make sure the painters tape you apply is long enough so it extends beyond the width of fabric. You will be cutting along the LOWER edge of the painters tape.
The set up is ready to start cutting.

Cutting area all set up ready to cutting (Photo makes the tape look skewed but it's really straight)

Cutting the fabric

Cut a straight edge at the top of the fabric with your quilting ruler before you set it on the floor.
Place the straightened edge of the fabric on the floor, matching the fabric edge with the LOWER edge of the painters tape, and run the fabric yardage across the floor and over the cutting mat. Check to make sure the top of fabric hasn't wiggled away from edge of the tape at the top of your cutting area.
Place a ruler over the fabric on the mat, lining it up with the LOWER edge of the tape used to mark the cutting line on the mat. (My fabric was 60 wide so I needed to use 2 rulers to reach across the width of fabric). Cut across the width of fabric with a rotary cutter.
Repeat to until all the lengths needed are cut.

Note how the cut edge of the fabric matches the LOWER edge of the painters tape

The fabric I was given for this project was polyester....very slippery stuff! It was really difficult to iron because it kept sliding off the ironing board.

I solved that problem by putting a folding table on next to my ironing board on the opposite side from where I was standing. That table was really helpful when the panels of the curtains were sewn together and got heavier and larger.

Table placed on the far side of the ironing board to support the weight of the fabric and help keep it on the ironing board

Hope these tips help with your project!